International application WO 01/72572 describes a wheel support system which allows a degree of wheel camber freedom relative to the suspension elements. This degree of freedom is controlled either actively, for example by a jack as a function of running parameters of the vehicle, or passively by the forces exerted on the wheel in the contact area.
The European patent application published under number EP 1232852 also concerns such systems and, to guide the camber movement of the wheel, proposes the use of an element which pivots about an essentially vertical axis articulated between the wheel support and the suspension elements.
The European patent application filed under number EP 02/013797.2 also concerns such systems and proposes to use a curved slide to guide the camber movement of the wheel support relative to the suspension elements.
One of the difficulties met in the design of these systems stems from the fact that large forces have to be transmitted from the road to the body (and vice-versa) via the ground contact system and in particular the tyre, the wheel support and the suspension. These forces produce large mechanical stresses with all the consequences that follow for the steering precision of the wheel and for the reliability of the systems. Viewed from the body of the vehicle, the forces transmitted by the road are generally expressed as follows: a transverse force (horizontal and perpendicular to the wheel plane), a longitudinal force (horizontal and parallel to the wheel plane, a vertical force, a torque known as the “spin” torque (around the axis of the wheel), a torque known as the “overturning” torque (around the longitudinal axis) and a torque known as the “self-alignment” torque (around the vertical axis). Besides these forces transmitted by the road, the wheel also transmits to the body forces stemming from the inertial forces imposed upon it, in particular the centrifugal force acting around curves.
In the support and suspension systems described in the patent applications cited earlier, an extra degree of freedom has been added compared with conventional suspension systems to allow a camber movement of the wheel relative to the body. This extra mobility can be provided in several different ways but they all have in common that increasing the number of components and joints or pivots tends to reduce the rigidity and/or robustness of the system as a whole. Moreover, it is difficult to compensate this rigidity deficit by increasing the cross-section of the various elements because the space available is generally restricted. In effect, such variable-camber suspensions should preferably not interfere with the compromises established in the context of space occupied (the term “packaging” is also used).
One problem with such systems is therefore to perfect their rigidity, in particular against the longitudinal force and the self-alignment and spin torques.
Another problem that can arise, especially in the systems described in EP 1232852, is the undesirable influence of certain types of force on the camber and particularly on the steering of the wheel plane.